Electric flash welding



Nov. 4, 1952 w, HEATH 2,617,004 7 ELECTRIC FLASH WELDING Original FiledMarch 26, 1943 IIIIIJ 4 IN V EN TO W/% k\\\\\ WiZZiczmOH h BYQWMQLMATTORNEYS.

Patented Nov. 4, 1 95 2 UNITED STATES ATENT OFFICE ELECTRIC FLASHWELDING William C. Heath, Milwaukee, Wis., assignor to A. O. SmithCorporation, Milwaukee, Wis., a corporation of New York Originalapplication March 26, 1943, .Serial No.

480,682. Divided-and this application December 23, 1949, .Serial No.134,745

2 Claims. 1

This invention relates to electric flash welding and to dash weldedjoints produced thereby.

The principal object of the invention is to provide for a reduction inthe flash extrusion at the welds in an electrically flash weldedarticle.

Another object-of the invention is to improve the metallurgy of the weldandprovide a weld of more uniform constituency having more nearlythe'characteristics of the parent metal stock Another object is toreduce and substantially eliminate the problem-of flash sputter stickingto the plate stock in regions remote from the weld and to the Weldingdies.

The invention has been applied to the'manufacture of hollow steelairplane propeller blades, and constitutes subject matter divided out ofapplicants copending application Serial No. 480,682, filed March 26,1943 (now abandoned), for Electrically Welded Hollow Steel PropellerBlade and Method of Making the Same.

In the manufacture of suchpropeller-blades by electric flash welding itis desirable to obtain a flash extrusion at the seam which is at leastsomewhat friable and easy to remove, particularlyin the narrow confinesof the inside of the blade. Furthermore, it is also desirable 'iIlSllChmanufacture to obtain a flash welded joint which has metallurgical andphysical characteristics as near to those of the plate stock aspossible,

The problem of removal of flash extrusion at the seam of electricallyflash welded articles has been well known-and articles such as propellerblades which have to bemade to close-tolerances as to balance and haverelativelynarrow'internal dimensions making flash removal additionallydifiicult have generally'been considered impossible of manufacture byelectric flash welding.

In carrying out the present invention a new principle in electric flashwelding is employed, 1. e. the utilizing of a stock alloy which has agreater strength at temperatures within the plastie range of the metal,whereby the amount of flash extrusion is greatly reduced and therelatively thin extrusion is readily cut for removal without danger ofinjuring the remaining weld. The thin fiash extrusion has a tendency tobecome air quenched by rapid cooling after welding and tobe brittle andeasily'removed, as compared to relatively thick and tougher flash extru-SlOIlS.

Steels containing small amounts of vanadium, molybdenum or chromium, orany combination thereof, have been found to have the characteristicsdesired for the practice of the present invention.

With such alloy steels, the greater strength of the metal in the plastictemperature range provides agreater resistance to upset and thereby morereadily transmits the welding pressures to the'meeting edges between theparts being welded without pronounced upset of the metal adjacent theedges. A more narrow band of fluidity is obtainable upon the edges andless carbon or alloy segregation is obtained in the final joint thanwith plain carbon steels and the like,

The invention is illustrated as applied to the electric flash welding ofa propeller blade.

In the drawings:

Figure .1 is-an isometric view of the partsprior to assembly by welding;

Fig. 2 is a plan view of the finished welded blade after machining andbalancing;

Fig. 3is a central longitudinal section taken on line 33 of Fig. 2;

Fig. 4 is a central transverse section taken on line 3-4 of Fig.2;

Fig. 5 is a typical enlarged central transverse section .showing atrailing edge and the foils clamped in position for welding;

Fig, 6 is a similar section taken immediately after .Weldingand prior tothe flash removal;

Fig. 7 is similar to Fig. 5 showing the welding of the leading edge tothe foils;

Fig. 8 is similar to Fig. 6 showing the welds between the leading edgeand the two foils prior to flash removal; and

Fig. 9 is a transverse section of the completed central body sectionafter welding and flash removal,

The blade 1 illustrated is made in a plurality of sections and which maybe described as a shank section 2, a body section 3, a tip section l andan end tip-5, all ofthe sections being electrically flash weldedtogether along transverse lines to complete the blade.

The several blade sections 2, 3, i and 5 may be formed as described inthe copending application referred to above. For the purpose ofillustration, the bodysection 3 is constructed of four parts: theleading edge forging 5, the trailing edge forging l, the camber face 3and'the thrust face 9. The several parts t, 5, ii andt are electricallyflash welded together along generally longitudinal lines to.cornpletethe body section.

.The formation ofparts 5, l, 8 and 9 is described more particularly inthe copending application referred to above and need not be repeatedhere.

In the electric flash welding operations the parts are clamped inwelding electrodes It, as shown in Figs. 5 and 7, with their respectivecomplementary edge potrions ii and I2 projecting toward one another andaligned for welding. The welding potential is applied and the respectiveopposing edges are moved toward each other until a flashing arc is setup by the current passing from edge to edge. The continued feeding ofthe parts relatively toward each other is governed in accordance withthe flashing off of the metal at the edges and when a sufflcient heatinof metal immediately adjacent the edge faces is attained, the remainingedges are abutted under pressure and the welding current discontinued.Generally, from one-eighth to one-quarter of an inch of metal isconsumed by the flashing off of metal from each edge, and the parts areconstructed with sufilcient additional metal at the edges to compensatefor this and for the extrusion of metal at the joint in the final bump.

In flash welding a much higher temperature of the metal on the opposededge surfaces is reached than in ordinary electric resistance welding.This is true because flash welding employs a heating of the edgeswithout pressure contact therebetween and involves the melting andsubsequent expulsion of preliminary contacting edge portions by thesudden super-heating and gasification of constituents of the contactingmetal. The above described expulsion occurs in rapid successiveexplosions of the highly heated metal particles all along the edges assoon as the flashing process has been established throughout the edges.At the time of the final bumping of the edges together under pressurethe fluid metal layer at the meeting faces of the edges is extrudedunder pressure laterally from the joint carrying with it most of theoxides that may be present.

Upon completion of the longitudinal electric flash welding operationsbetween the trailing edge forging l and the foils 3 and 9 the flashextrusion I3 is removed from both the inside and outside, preferably bya chisel or other suitable tool, and then the seam is dressed as by abelt sander or other device to smooth the same in line with the contourof the parts. Following this operation, the leading edge forging 6 iselectric flash welded to the remaining longitudinal edges of the foils 8and 9 and the welds cleaned in the manner above described. Where thematerial of the blade or other article has a tendency to harden at theline of the Weld it may be advisable to remove the hardness by a partialanneal before removal of the flash.

In carrying out the present invention, a relatively high strength lowalloy steel is employed. The steel employed has a greater strength inthe plastic temperature range than ordinary steels. It is also possiblethat it has a lower melting point than ordinary steel thereby tending toproduce a more narrow band of plastic metal adjacent the weld line.

These factors combined with the sharper line of strength gradient ofthis alloy at the zone between the plastic and fluid temperature rangesresult in an extrusion of the flash it in a very narrow line at the Weldand make it comparatively easy to chisel the flash from the weld.

The higher strength of this alloy in the plastic temperature rangeenables the transmission of the requisite welding pressure to the jointwithout the accompanying extrusion of a substantial part of the plasticmetal immediately behind the fluid surface layer, as compared to theflash welding of ordinary steel. This results in a narrow line ofextruded metal and becomes 4 important in the manufacture of propellersdue to the fact that the flash on the inside of the blade is relativelyinaccessible and therefore ordinarily diflicult to remove.

Furthermore, the narrow line of flash is obtained under conditions ofbump and pressure giving a very high quality weld. A higher bumppressure may be employed.

The blade or other article may be composed of an alloy of the followingcomposition:

Percent Carbon .35-.40 Manganese .60-.80 Nickel 1.65-2.00 Chromium.70.90 Molybdenum .20-.30 Silicon .35 maximum Copper .25 maximumPhosphorus .04 maximum Sulphur .04 maximum Balance iron.

A small percentage of vanadium, up to about 20%, may be employed, ifdesired.

Other alloys may be employed that will tend to reduce the thickness offlash and thereby facilitate its removal. In general, vanadium,molybdenum, chromium and to some extent nickel, when added to steel insmall amounts, will have the effect described of producing a narrow lineof flash by raising the strength of the metal in the plastic temperaturerange. These alloy ingredients may be used alternatively or in anydesired combination depending upon the characteristics of the steeldesired for the article to be welded.

By reason of the characteristics of the alloy the weld sputter in theform of condensed globules of flash which are expelled from the edgeshas less tendency to stick or fuse to metal objects, such as the partsbeing welded and the welding electrodes, upon which it falls. Thegreater strength of the sputter globules reduces the flattening of theglobules against the metal surface, and any interfusing that occurs isover a smaller area, making removal a relatively easy matter.

In the manufacture of propellers and the like it is highly important toavoid the sticking of sputter to the inside surfaces of the pieces beingwelded. Sputter, when welded to the surface of the parts, is extremelydifiicult to remove, and if not removed it may seriously hamper thebalancing of the blade.

While the alloy content of the metal makes for less softness of thesputter and consequent less tendency of it to stick, it is desirable toprevent sticking of the sputter as by employing a coating l4 on theparts and on the adjacent welding electrodes.

A suitable composition for coating M to prevent the welding of sputterto the surface of the parts contains a large amount of magnesium andcalcium silicates with calcium oxide and a small amount of graphite.Various compositions may be employed within the scope of the invention,the essence lying in providing a material with refractory ingredientswhich prevent sticking of the sputter to the parts.

Various embodiments of the invention may be employed within the scope ofthe accompanying claims.

I claim:

1. An electrically flash welded article, comprising a plurality ofsections of low alloy steel containlng a small percentage of a flashreducer UNITED STATES PATENTS selected from the following metals:vanadium, Number Name Date molybdenum and chromium. 7 1,958,153 Budd May8, 1934 2. In the manufacture of metal articles by 2,014'240 Tarbox eta1 Sept 10 1935 electric flash welding, the forming of parts of the 52,085 533 Hanson June 26, 1937 article from 10W alloy steel containing asmall 22781497 Rakes Apt 7' 1942- percentage of one or more of thefollowing ingradients: vanadium, molybdenum and chro- FOREIGN PATENTSmium; electrically flash welding a seam between Number Country Date twoof said parts, and thereafter cleaning the 10 200,952 Great Britain July26, 1923 flash from both surfaces of said seam. 797,762 France Feb. 24,1936 WILLMM HEATH' OTHER REFERENCES REFERENCES CITED Woldman andMetzler, Engineering Alloys,"

The following references are of record in the 15 1945 editionfile ofthis patent:

2. IN THE MANUFACTURE OF METAL ARTICLES BY ELECTRIC FLASH WELDING, THEFORMING OF PARTS OF THE ARTICLE FROM LOW ALLOY STEEL CONTAINING A SMALLPERCENTAGE OF ONE OR MORE THAN THE FOLLOWING INGREDIENTS: VANADIUM,MOLYBDENUM AND CHROMIUM; ELECTRICALLY FLASH, WELDING A SEAM BETWEEN TWOOF SAID PARTS, AND THEREAFTER CLEANING THE FLASH FROM BOTH SURFACES OFSAID SEAM.